A high-risk result on the prenatal chorionic villus sampling test means that the patient’s unborn child has a genetic or chromosomal disorder, according to Mayo Clinic. This test is used to diagnose numerous genetic conditions such as Down syndrome, Tay-Sachs disease, cystic fibrosis, sickle cell anemia and some types of muscular dystrophy, says WebMD. It also identifies the child’s sex.
To perform the test, a small sample of chorionic villi cells is taken from the mother’s placenta where it connects to the uterine wall. The sample is taken through either the abdominal wall or the cervix. Chorionic villi are small placenta parts formed from the fertilized ovum that have the same genes as the baby, explains Mayo Clinic. The test is done between the 10th and 13th weeks of pregnancy.
A doctor may recommend a chorionic villus test if the mother has had a chromosomal condition in a previous pregnancy, is 35 years of age or older, or received positive results from a prenatal screening test, or if one or both parents are known carriers or have a family history of a genetic condition, says Mayo Clinic.
A chorionic villus test may cause a miscarriage or a uterine infection. The mother also risks Rh sensitization if the fetus’s blood cells enter the mother’s bloodstream during the test. If the mother has Rh negative blood and the baby has Rh positive blood, the mother might produce Rh antibodies, explains Mayo Clinic. In this case, the mother is injected with Rh immune globulin after the test to prevent her from creating antibodies that could harm the child.